The present invention relates to a medical image recording system for recording an image on a recording medium based on image information and, more exactly, to a medical image recording system for recording with ink-jet the medical image information obtained through an input device, such as a medical photographing device.
These years, there have been invented methods of obtaining medical radiographic information without using a radiographic film made of silver-salt photosensitive material. For example, computed radiography (CR) has become popular; it is a device for reading radiographic images, in which a radiographic image, once stored on an imaging plate comprising mostly of accelerated phosphor, is taken out as an accelerated emission light, using an excitation light, and then the light is photoelectrically transferred into an image signal.
Of late, there has been proposed a device called flat panel detector (FPD) that reads out radiographic information using radiation phosphor or radiation photo-conductive substance combined with a two-dimensional semiconductor detector such as a TFT switching device.
Besides, other radiographic image input devices better than simple radiography, for example, X-ray computer tomography unit (X-ray CT unit) and magnetic resonance image generator (MRI generator) have also come into wider use. Most of these medical image input devices provide the image information in the form of digital signals. A method most frequently employed for diagnosing these medical images is to record the image information on a transparent-type recording medium and/or reflex-type recording medium and observe the image in the form of a hard copy.
A recording method most frequently applied to a medical image recording device for recording the medical image information on a recording medium is to record an image on a transparent-type recording medium, made of silver-salt recording material, by laser exposure. With this method, monochrome multi-gradation image can be depicted with excellent gradient and besides, recording the image on a transmission medium and observing it with a transmission light enables to achieve high diagnostic resolution.
Besides, very recently, hopes are laid on a possibility of recording medical images using an ink-jet type recording device.
Conventionally, in most cases, while images used for diagnosis are recorded on transparent-type recording medium and observed with transmission light, images recorded on reflex-type recording medium are put on a clinical chart or used for explanation to a patient, that is, the images are recorded for reference purpose. These years, however, there have been increasing needs of using the reflection images in diagnosis because of the convenience.
Besides, even when used for reference purpose, there is a need that the image makes a similar appearance to a transmission image used actually for diagnosis.
Even if an image is recorded on a reflex-type recording medium in the same way as on a transparent-type recording medium, however, a reflection image does not have the same appearance as an transmission image because of higher density. If this difference is taken into account and suitable gradation processing is employed depending upon the type of the recording medium, the above problem can be solved to some extent.
That is, a solution is to process the images so that the reflection density and transmission density become approximately equal. Besides, as disclosed in the Japanese Application Patent Laid-open Publication No. HEI 10-202920 (1998), instead of performing different gradation processing depending upon the type of the recording medium, selecting the combinations of different ink densities can result in the same effect as produced in performing different gradation processing.
However, a satisfactory effect cannot be produced simply with the above method. Since a transmission image is observed in a transmitted state, using high-intensity light source, an influence of the light that reflects on the surface of the recording medium and comes into the observer's eyes is very small (See FIG. 7(a) and FIG. 7(c)). In addition, if lights are turned off in the room for observation, no reflected light is caused and only the optical density based on the optical absorption of colors can be observed.
A reflex-type recording medium, on the other hand, has some glossiness, much or less, on the surface and, even if sufficient amount of color is put on the recording medium, the density obtained from it is lower than the optical density based on the optical absorption because there exists reflected light of a light irradiated for observation (See FIG. 7(b) and FIG. 7(d)).
For the above reason, it is impossible to make the reflection density of a reflected image similar to the transmission density of a transmitted image in the high density range of the image. In addition, deterioration of sharpness on a reflex-type recording medium is more significant than on a transparent-type recording medium because the extent of light scattering inside the recording medium is greater, but this difference in the sharpness cannot be corrected even by different gradation processing. In other words, as shown in FIG. 7(e), the reflected image density (<1>) can be corrected to <2> or <3> but not to the transmitted image density (<4>) throughout the whole density range because of the highest reproducible density limit. Even if corrected to <2> to <3>, it is inevitable that the contrast in the high density range becomes lower or insufficient.